Means for controlling the leakage flux in transformers

ABSTRACT

In transformers for high power amounts, for collecting the leakage flux and leading it back to the iron core, plates of laminated magnetic material are arranged close to the ends of the winding coils and at least one end of the plates is in magnetic connection with the core.

United States Patent Hessen et al.

[54] MEANS FOR CONTROLLING THE LEAKAGE FLUX IN TRANSFORMERS [72] Inventors: Petter Hessen; Ruudi Siirak, both of Ludvika, Sweden Allmanna Svenska Elektriska Aktiebolaget, Vasteras, Sweden [73] Assignee:

[22] Filed: Dec. 31, 1970 211 App]. No.: 103,302

Related US. Application Data [63] Continuation of Ser. No. 866,881, Oct. 10, 1969, abandoned, Continuation-impart of Ser. No. 827,877, May 26, 1969, abandoned.

[30] Foreign Application Priority Data May 30, 1968 Sweden ..7242/68 [52] U.S.Cl ..336/84, 336/212 [51] 1nt.Cl ..H01t 27/24 [58] FieldofSearch ..336/84,212,214,215,219, 336/100, 210, 234

[56] References Cited UNITED STATES PATENTS 1,610,867 12/1926 Lennox 33 6/2 15 X 51 Feb. 1, 1972 2,550,500 4/1951 Schell, Jr. ..336/214 X 2,896,182 7/1969 Pruneau ..336/212 X FOREIGN PATENTS OR APPLICATIONS 886,135 6/1943 France ..336/2l5 49,944 10/1966 Germany ..336/212 366,467 1/1923 Germany ..336/2l2 6,805,831 10/1968 Netherlands ..336/2 1 2 440,442 12/1967 Switzerland ..336/212 OTHER PUBLlCATlONS Brown et a1., German App. No. 1,051,960 Pub1.3/5/59 Siemens et al., German App. No. 1,056,731 Publ. 5/6/59 Primary Examiner-Thomas J. Kozma Attorney.lennings Bailey, Jr.

[5 7] ABSTRACT In transformers for high power amounts, for collecting the leakage flux and leading it back to the iron core, plates of laminated magnetic material are arranged close to the ends of the winding coils and at least one end of the plates is in magnetic connection with the core.

PATENTED FEB 1 1972 SHEET 2 OF 3 Fig. #0

INVENTOR. PETTEQ HESSEN rzuum SHRAK BY M??? sfi MEANS FOR CONTROLLING THE LEAKAGE FLUX IN TRANSFORMERS This application is a continuation of application Ser. No. 866,881, filed Oct. l0, 1969, now abandoned; application Ser. No. 866,881 is a continuation-in-part of application Ser. No. 827,877 filed May 26, 1969, now abandoned.

BACKGROUND OF THE INVENTION 1 Field of the Invention The present invention relates to means for controlling the leakage flux in transformers for high power.

2. The Prior Art In transformers certain losses occur in solid constructional parts of iron, particularly in the tank walls because of leakage flux from the windings. In large transformers these leakage flux losses assume such a value that special steps are necessary to limit them and thus improve the efi'lciency of the transformer and also to a certain extent reduce the noise from those parts through which the leakage flux flows. I

SUMMARY OF THE DISCLOSURE In a transformer embodying the invention, plates of laminated magnetic material are arranged as end pieces for the parts of the transformer windings lying outside the yokes of the transformer core. One end of such pieces is magnetically connected to at least one part of the transformer core.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings:

FIG. 1 shows a vertical cross section through the upper yoke along the line 1-1 of FIG. 2.

FIG. 2 is a horizontal section through a core leg along the line IIII of FIG. 1.

FIGS. 3a and 3b show in views similar to FIGS. 1 and 2 a modification where the leakage flux plate is composed of a number of partial plates.

Another modification of the invention is shown similarly in FIGS. 4a and 4b where the leakage flux plates are composed of L-shaped strips.

FIGS. 50 and 5b show in the same way a construction using plates that are composed of two parts connected to each other along a butt joint.

FIGS. 6a and 6b show similarly the strips of the plate interleaved with each other.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1 the upper yoke is denoted 1. The yoke is held under pressure in the horizontal direction with the help of the pressure beam 3. At the lower end of the pressure beam a number of support flanges 4 are fastened to the pressure beam by welding and they are braced with the help of cross braces 5. Below the support flanges there is a plate 6 of insulating material, the task of which is to equalize the pressure force from the windings against the support flanges. A plate 7 of insulating material is also inserted between the yoke l and the pressure beam 3.

In FIGS. 1 and 2 the low-voltage winding is denoted 8 and the high-voltage winding 9. A tube 10 of insulating material is arranged outside the core leg 2 as indicated in FIG. 2, and a tube 11 is arranged outside the winding 9. Oil channels are arranged between the tube 10 and winding 8 between the two windings and between winding 9 and tube 11. This is common and therefore not specially indicated on the drawing. Above the ends of the two windings there is an insulating ring consisting of two ring-shaped plates 12 and 13. The inner diameter of the rings is about the same as the inner diameter of the tube 10 and the outer diameter is about the same as the outer diameter of tube 11. The two rings are separated by a number of spacers 14 arranged radially as seen in FIG. 2, thereby providing oil channels 15 between the space inside tube 10 and the space outside tube 11.

Between the insulating ring and the plate 6 two plates 16 are arranged on each side of the yoke 1. In FIG. 2 the shape of the two plates on one of the core sides is shown. The plates are built up of a number of vertical strips of sheet metal, preferably transformer steel plate, which are placed close to each other and preferably glued together in order to obtain a stable construction.

The shape of the plates may vary in many ways and those of FIG. are rhomboidal so that they cover the greater part of the ends of the windings outside the yoke. The triangular area between the two plates and the leg is filled out with a triangular plate 17 of insulating material to support those parts of the windings which are not supported by the leakage flux plates 16.

Between the upper surface of the plates 16 and the lower side of the plate 6 narrow strips 18 of insulating material are situated so as to provide channels for the cooling oil.

On both sides of the leg, where the leg is interleaved in the yoke, there are two recesses 19 in the yoke, as is seen in F IG.- 1. A vertical plate 20 of insulating material is arranged along the inner wall of this recess in order to prevent the inner ends of the strips of the leakage flux plates 16 from coming in contact with the laminations of the yoke. Without this insulating plate the strips in the leakage flux plates would be short-circuited by the outermost steel plate in the yoke and this would result in an overheating in the contact surface.

The task of the leakage flux plates is to collect the leakage flux between and outside the windings and lead it back to the core. However, the flux must be led into the core through the cut edges of the steel plates in order to avoid eddy currents. Therefore two connection plates 21 and 22 of steel plate are laid on the upper side of the inner ends of the leakage flux plates 16 between said ends and the lower side of the outer part 23 of the upper yoke. Thin insulating plates 24 and 25 are inserted above and below the connection plates 21 and 22 to prevent direct contact between the leakage plates 16, the plates 21, 22 and the yoke part 23.

The leakage flux that appears inside the winding 8, outside the winding 9 and between the two windings goes upwardly through the oil channels between the spacers l4 and enters the leakage flux plates 16, then turns to the left but is prevented from entering the yoke in the horizontal direction by the plate 20 and is therefore bent upwardly and enters the yokethrough the insulating plate 25, the plates 21 and 22 and then the insulating plate 24. Beside this essential task, the leakage flux plates provide effective mechanical support for the ends of the windings and thus fulfill two important purposes j The plates may be in one piece as shown in FIG. 2, or divided into a number of narrow parallel partial plates, as will be explained later.

The fact that the steel plates of the connection plates 21 and 22 abut not only the plates in the outer part 23 of the yoke, but also the plates of the core leg 2 through insulating plates 26 and 27 gives a great contact area on the complete transformer core and consequently a small reluctance for the flux.

The strips or plates 21, 22 are not, however, essential, and can be omitted, in which case there is no upward extension of recess 25 and the laminations of the yoke engage directly through a thin layer of insulation on the laminations 16.

In FIG. 2 the leakage flux plates 16 are compact rhomboidal units. FIGS. 30 and 3b show a modification where the plates are composed of a number of partial plates 161, 162, I63 and 164 with narrow openings between them. Preferably the connection plates 21 and 22 are similar to those of FIG. 2.

FIGS. 4a and 4b show the strips in the leakage flux plates and the strips in the connection plates 21 and 22 m e in one piece Such a strip has an L-fonn where the long part 165 forms the leakage flux plate and the short part 166 forms the connection plates 21 and 22.

In the modification shown in FIGS. 50 and 5b the leakage flux plate 16 is composed of two parts 167 and 168. The two parts are shaped with a straight edge which forms an angle to the longitudinal direction of the strips in the parts and the two strips, there is no appreciable increase in reluctance in the I leakage flux plates.

A further, somewhat modified, leakage flux plate is shown in FIGS. 6a and 6b. Here the plate is composed of bent strips and straight strips. The bent strips, one of which is denoted 30, have one part in magnetic connection with the plates in the transformer leg. The other part reaches into the real leakage flux plate 16, where it is continued by a straight strip 31 with a butt joint 32. These straight strips are interleaved with long strips 33 which reach from the free end of the leakageiflux plate to the bending point of the bent strips.

We claim:

1. An electrical transformer comprising a magnetic core and windings, the core having yokes and core legs, said windings being arranged around the legs, parts of the end faces of the windings being outside the yokes, a pressure beam on each of the two opposite sides of the yokes in line with the legs, each pressure beam having a flange perpendicular to said two opposite sides of the yokes, said flanges facing one end of the windings with a space between the flangeand the corresponding end-of the windings, leakage flux collecting means comprising at least one plate of laminated magnetic material situated in said space between the flange and an end of each of the windings, the laminations of said plate extending outward from the yoke at a substantial angle to the longitudinal direction of the pressure beam and extending substantially to the periphery of the windings, said collecting means covering the greater'part of the end faces of the windings lying outside the yokes, a portion of the yoke which overlies the windings having at least one elongated recess therein opening towards the pressure beam and located in the inner part of the yoke so i that outerparts of the yoke overlie the recess, the longitudinal 

1. An electrical transformer comprising a magnetic core and windings, the core having yokes and core legs, said windings being arranged around the legs, parts of the end faces of the windings being outside the yokes, a pressure beam on each of the two opposite sides of the yokes in line with the legs, each pressure beam having a flange perpendicular to said two opposite sides of the yokes, said flanges facing one end of the windings with a space between the flange and the corresponding end of the windings, leakage flux collecting means comprising at least one plate of laminated magnetic material situated in said space between the flange and an end of each of the windings, the laminations of said plate extending outward from the yoke at a substantial angle to the longitudinal direction of the pressure beam and extending substantially to the periphery of the windings, said collecting means covering the greater part of the end faces of the windings lying outside the yokes, a portion of the yoke which overlies the windings having at least one elongated recess therein opening towards the pressure beam and located in the inner part of the yoke so that outerparts of the yoke overlie the recess, the longitudinal direction of elongation of the recess being parallel to the longitudinal direction of the pressure beam, the end of the plate extending into and being supported in said recess.
 2. A transformer according to claim 1, in which the plates are of polygonal shape. 